In bottle feeding an infant, care must be taken to ensure that the bottle's nipple constantly remains full of liquid in order to prevent colic or distress to the infant due to the ingestion of air during the nursing process. Accordingly, during bottle feeding, the bottle is customarily held in a semi-inverted, nipple-down position so that the fluid will fill the nipple and any air in the bottle will retreat to the opposite end of the bottle. The angle at which the bottle is held, and to some extent the angle of the infant's head as well, tends to vary during the feeding process in order to ensure the continuous presentation of a full nipple to the infant.
More specifically, at the start of feeding, when the bottle is substantially full of liquid, the infant's head is typically tilted upward at an angle to prevent choking and for improved peristalsis, while the bottle is held with its longitudinal axis inclined at a small upward angle so that the nipple resides below the opposite end of the bottle. Since the bottle is at its fullest, and hence heaviest, at this point in the feeding process, this position tends to be the most comfortable for the individual feeding the infant. At the same time, however, since there is relatively little air in the bottle at this point, there is little chance of the infant ingesting air with this almost-horizontal bottle orientation.
As the feeding progesses, however, the ratio of air to liquid in the bottle increases. As a result, in order to avoid unintended ingestion of air from the bottle, the bottle's angle of inclination must gradually be increased, while the angle of inclination of the infant's head is gradually decreased, so as to ensure that only fluid will be ingested by the infant. This process continues until, at the conclusion of feeding, the bottle generally approaches a substantially vertical, fully-inverted orientation, while the infant's head generally approaches a substantially horizontal orientation.
It has also been found desirable to monitor the amount of liquid remaining in the bottle during the feeding process. This enables the individual feeding the infant to maintain control over the amount and rate of liquid ingested by the infant, and to know if the baby is actively feeding or if it is just pacifying itself on the nipple. This can be of particular interest when evaluating a new nipple to determine if the nipple hole size is appropriate or, when enlarging an existing nipple hole, to determine if the nipple hole size has been enlarged enough.
To this end, traditional nursing bottles frequently have graduated markings disposed on the side of the bottle to indicate the volume of liquid contained in the bottle. These graduated markings traditionally extend parallel to the bottom of the bottle and are sequentially numbered, with the lowest number set at the bottom end of the bottle (i.e., at the end opposite the nipple) and the highest number set at the top end of the bottle (i.e., at the end adjacent the nipple). In this way such bottles can be set upright and the amount of fluid remaining in the bottle read by simply comparing the meniscus of the fluid to the graduated markings.
Unfortunately, such bottles require that the individual feeding the infant periodically interrupt the infant's feeding and return the bottle to its upright position in order to determine the amount of fluid remaining in the bottle. Such interruptions of the infant's feeding are, of course, undesirable, particularly since it is often difficult or impossible to make the infant resume feeding thereafter.
See, for example, U.S. Pat. No. 3,332,563. Similar arrangements for other types of containers are shown in U.S. Pat. Nos. 1,203,448 and 3,645,413.
To solve this problem, it has been suggested that traditional nursing bottle be provided with markings located in parallel, downwardly slanted planes extending through the bottle. These markings can be provided either alone (as shown in U.S. Design Pat. No. 167,914), or in combination with a nipple having an oblong cross-section, the major transverse axis of which is located parallel to the planes containing the graduated markings on the bottle (as shown in U.S. Pat. No. Re. 25,247).
Similarly, it has been suggested in U.S. Pat. No. 2,514,744 that a bottle be provided which is adapted to be placed on its side such that its longitudinal axis extends at a small angle to the horizontal, and which has an open mouth positioned at the lower end of the bottle which faces downward when the bottle is so positioned. The liquid-containing chamber of this bottle is configured in such a way that a nipple attached to the open mouth of the bottle will remain full of fluid throughout the feeding process, without any tipping of the bottle. Parallel graduated markings are provided on the side of this bottle for measuring the amount of liquid remaining in the bottle during feeding.
Furthermore, means have been proposed for monitoring the fluid flow through a nipple, such as those shown in U.S. Pat. No. 3,790,016.
Unfortunately, none of the foregoing arrangements has proven to be totally satisfactory.
Slanted parallel markings positioned on the side of a traditional nursing bottle (e.g. as in the case of U.S. Design Pat. No. 167,914 or U.S. Pat. No. Re. 25,247) generally do not provide helpful or convenient indications of the amount of fluid remaining in the bottle during feeding, since they assume a generally constant bottle orientation during feeding. Unfortunately, however, as noted above, in practice the bottle's angle of orientation tends to vary during feeding, with the bottle's nipple being gradually tipped further and further downward until the bottle reaches a substantially vertical orientation. Thus, providing a plurality of parallel slanted markings on the exterior of the bottle cannot provide accurate indications of the amount of fluid remaining in the bottle over the wide range of bottle orientations encountered in feeding.
The bottle of U.S. Pat. No. 2,514,744 is designed primarily for use in the situation where the bottle is placed on a flat surface, with the nipple overhanging an edge thereof, so that an infant may take the nipple in its mouth and nurse, without the bottle being held by an individual. Such unattended nursing is generally not preferred; an adjacent overhanging edge may not be conveniently available; and the configuration of the bottle is generally uncomfortable for traditional feeding.
Finally, fluid monitoring devices are generally relatively expensive, cumbersome, and subject to malfunction if not carefully maintained.
U.S. Pat. No. 388,677 discloses an open mouthed container with measurement lines which radiate outwardly from the pouring point of the container. These lines are located such that as the container is rotated to allow the liquid contained therein to spill out over the pouring point, a means is provided for determining the quantity of liquid remaining in the container without interrupting the pouring operation or returning the container to its upright position.
It must be appreciated, however, that the act of pouring fluid out of an open-topped bottle is substantially different from the act of infant feeding with a nipple-topped bottle. Specifically, in pouring one always wants air to be able to enter the container continuously through the container's open mouth, above the liquid stream flowing out of the container. If this does not occur, the liquid will not flow smoothly and continuously out of the container. Conversely, however, in bottle feeding, one always wants the nipple and the open mouth of the bottle to remain full of liquid so as to ensure that only liquid is ingested by the infant. Accordingly, with many infant bottles air is introduced into the bottle to replace the liquid consumed by the infant through small, one-way valves located at the base of the nipple so that the air will bubble upwardly through the liquid in the semi-inverted container. Alternatively, some infant bottles place the liquid in a flexible inner pouch which can contract in volume as the fluid is removed, so that no air need be introduced into the pouch as the fluid is removed. In either case the goal is the same; to provide means by which feeding can occur while the nipple is kept continuously full of fluid.
Thus it will be appreciated that, inasmuch as an air gap would always be presented at the open mouth of a container such as that taught in U.S. Pat. No. 388,677, such a container is not applicable for use in a bottle feeding context.
Still other fluid level indicators for containers are shown in U.S. Pat. Nos. 3,077,279 and 4,293,084. However, such arrangements are not believed to be satisfactory for use in continuously monitoring the fluid level in a baby bottle during the typical feeding process discussed above.